Numerical simulation of optimization the NCF dimension based on spectral response in optic filter

Tunable fiber lasers play an important role in many optical fiber communication and optical fiber sensing applications. Over the past few decades, various types of tunable fiber lasers have emerged because of their benefits, which include a changeable output wavelength, a greater beam quality, and high integration. One of the most important components of tunable fiber lasers is the fiber filter-based multimode interference (MMI), which is an attractive filter due to its relatively wide tunability range, simple design, and compactness. This optical filter has been constructed using different fibers’s dimensions. In the present work, the MMI filter based on no-core fiber (NCF) has been designed. In the simulated model, the MMI filter is formed by incorporating a short length of NCF between two single-mode fibers. The influence of NCF lengths and diameters has been studied. The simulated model is supported by simulation results obtained using COMSOL 6.1 multiphysics software. The simulated results show that the NCF diameters have an observable influence on tunability; the maximum tunability was 200 nm at D_NCF = 60 μm when D_NCF changed from 58 µm to 62 µm. The corresponding maximum tunability for three different NCF lengths of MMI filters when L_NCF is changed from 14 to 15 mm, 5.5 mm to 6.5 mm, and 3 mm to 4 mm are 105, 255, and 400 nm, respectively.